Ash fusing system, method of operating the system, and gasification fusing system for waste

ABSTRACT

An ash melting system of the present invention includes a slagging combustion furnace ( 10 ) for melting ash into molten slag; and a slag separating apparatus ( 50 ) for bringing the molten slag ( 121 ) discharged from the slagging combustion furnace into contact with slag cooling water ( 152 ) to produce water-quenched slag ( 122 ), and separating the water-quenched slag from the slag cooling water. The ash melting system further includes a gas blowing means for blowing air or inert gas ( 132 ) between a slag discharge port ( 14 ) of the slagging combustion furnace and the surface of the slag cooling water.

TECHNICAL FIELD

The present invention relates to a melting system for bringing themolten slag discharged from an ash melting furnace into contact withwater to produce water-quenched slag and a method of operating suchmelting system, and a melting system attached to a gasification andslagging combustion system for combusting various wastes includingmunicipal wastes, refuse-derived fuel (RDF), plastic wastes, waste FRP,biomass wastes, automobile wastes, waste oil, and the like.

BACKGROUND ART

It has been desired that wastes including municipal wastes,refuse-derived fuel (RDF), plastic wastes, waste FRP, biomass wastes,automobile wastes, waste oil, and the like are safely combusted toreduce the volume of the wastes, and the combustion heat of the wastesis effectively utilized. Because incineration ash usually containsharmful heavy metals, in order to reclaim the incineration ash, it isnecessary to take some measures for stabilizing heavy metal components.Further, there has been a request for downsizing a waste treatmentfacility as a whole. In order to realize the above subjects, agasification and slagging combustion system which can recover variousmetals and harmless slag capable of being effectively utilized, andrecover energy in the form of heat, electric power or the like has beenput to practical use. The gasification and slagging combustion system isnot ordinary incineration, but is capable of performing material andthermal recycling.

In the gasification and slagging combustion system, wastes are pyrolyzedand gasified at a temperature of 450 to 750° C. to generate a gas, tar,char (solid carbon containing ash), and the like in the gasificationfurnace, and the generated gas and tar are introduced into the slaggingcombustion furnace together with particulate char and combusted by asecondary air at a high temperature under a low air ratio of about 1.3to about 1.5 to increase a combustion temperature of a melting point ofash or higher (for example, 1300° C. to 1450° C.) in the slaggingcombustion furnace. In this high-temperature condition, molten ash iscollected on a furnace wall surface and falls along the furnace wallsurface, thus forming a flow of molten slag. This molten slag iscontacted with cooling water to form water-quenched slag.

An ash melting system does not have a gasification furnace. In the ashmelting system, ash is supplied directly to a melting furnace to producemolten slag. The process in which molten slag is converted intowater-quenched slag is substantially the same as the above gasificationand slagging combustion system. Therefore, details of the ash meltingsystem will not be described here.

Next, a combination of a gasification apparatus comprising afluidized-bed gasification furnace and a slagging combustion furnacecomprising a swirling-type slagging combustion furnace will be describedbelow. FIG. 1 shows a conventional melting system having a swirling-typeslagging combustion furnace and a water quenching trough, and a slagseparating apparatus for separating molten slag.

In FIG. 1, reference numeral 10 represents a swirling slaggingcombustion furnace (swirling-type slagging combustion furnace),reference numeral 30 represents a water quenching trough, and referencenumeral 50 represents a slag separating apparatus. The swirling-typeslagging combustion furnace 10 comprises a primary combustion chamber11, a secondary combustion chamber 12, and a tertiary combustion chamber13. A produced gas (combustible gas) 111 containing char and tar whichhas been generated by pyrolysis and gasification in a gasificationfurnace (not shown) is introduced into the upper part of the primarycombustion chamber 11 tangentially to an inner wall surface of theprimary combustion chamber 11. Then, the gas 111 is mixed with a gas forcombustion (usually, preheated air) 115 introduced into the primarycombustion chamber 11, and is combusted and flows into the secondarycombustion chamber 12 where the gas is combusted at a high temperatureof about 1300 to about 1450° C. Then, the gas flows into the tertiarycombustion chamber 13 and is completely combusted, and resultantcombustion exhaust gas 113 is then supplied to a waste heat boiler (notshown). In FIG. 1, reference numerals 15 and 16 represent a burner forstartup and auxiliary heat supply of the slagging combustion furnace,respectively.

The generated gas 111 containing char and tar which has been introducedinto the upper part of the primary combustion chamber 11 forms aswirling flow, and moves to the secondary combustion chamber 12 while itis combusted at a high temperature in the swirling flow. Undercentrifugal forces by the swirling flow, ash contained in the char ischanged to slag mists and collected on the furnace wall surface. Theslag mists attached to the furnace wall surface form a layer of moltenslag 121, and the molten slag 121 flows down the bottom of the secondarycombustion chamber 12, then falls from a slag discharge port 14 onto thewater quenching trough 30. Water for cooling molten slag (hereinafterreferred to as slag cooling water 152) flows on the water quenchingtrough 30 at all times. The molten slag 121 which has fallen from theslag discharge port 14 is dropped into the slag cooling water 152 andquenched to form water-quenched slag 122. The water-quenched slag 122flows together with the slag cooling water 152 into a water tank 51 ofthe slag separating apparatus 50. The water tank 51 has a slag settlingfunction. The settled water-quenched slag is scraped and removed byscrapers 53 attached to a separating conveyor 52, and is carriedupwardly and separated from the slag cooling water. The water-quenchedslag 122 is then discharged from the separating conveyor 52 through aslag discharge opening 54 to the outside of the slag separatingapparatus 50. The slag cooling water 152 in the water tank 51 isdelivered by a pump 41 from the water tank 51 onto the water quenchingtrough 30 through a pipe-line 151 and a nozzle 32. The slag coolingwater 152 is circulated and reused.

The slag discharge port 14 serves to discharge molten slag 121 from theswirling-type slagging combustion furnace 10. However, because theswirling-type slagging combustion furnace 10 is filled with the exhaustgas 112, the molten slag 121 accompanies the exhaust gas 112 which isunavoidably going to contact the slag cooling water 152. Since theexhaust gas 112 contains many components including harmful substances,the exhaust gas 112 tends to contaminate the slag cooling water 152 anddeteriorates the quality of the slag cooling water 152 by beingcontacted with the slag cooling water 152. As a result, the recoveredwater-quenched slag 122 is contaminated by the slag cooling water 152.

When the high-temperature molten slag 121 contacts the slag coolingwater 152, a part of the slag cooling water 152 is evaporated, and thegenerated steam goes up to cool the slag discharge port 14.Consequently, the molten slag 121 is liable to be solidified on theinner surface of the slag discharge port 14 and the portion around theslag discharge port 14, and in extreme cases, the slag discharge port 14is clogged with the solidified slag.

SUMMARY OF THE INVENTION

The present invention has been made in view of the above drawbacks. Itis therefore an object of the present invention to provide an ashmelting system, a method of operating a melting furnace apparatus, and agasification and slagging combustion system, for producingwater-quenched slag by bringing molten slag discharged from a slaggingcombustion furnace into contact with slag cooling water, which canprevent exhaust gas discharged together with the molten slag from theslagging combustion furnace (melting furnace) from contacting the slagcooling water, prevent a slag discharge port and a portion around theslag discharge port from being cooled by steam evaporated from the slagcooling water, and prevent the water-quenched slag from being made worsein quality due to a deterioration in the quality of the slag coolingwater (if the slag cooling water is contaminated, the contaminated slagcooling water is adhered to the surface of the slag granules to cause adeterioration in the quality of water-quenched slag).

Another object of the present invention is to provide a cleaning systemfor removing harmful contaminants such as heavy metals which may havebeen adhered to the surfaces of water-quenched slag granules, even ifexhaust gas discharged together with molten slag from a slaggingcombustion furnace is not fully prevented from contacting slag coolingwater.

In order to achieve the above objects, according to the presentinvention, there is provided an ash melting system comprising: aslagging combustion furnace for melting ash into molten slag anddischarging the molten slag from a slag discharge port; a slagseparating apparatus for bringing the molten slag into contact with slagcooling water to produce water-quenched slag, and separating thewater-quenched slag from the slag cooling water; and a gas blowing meansfor blowing air or inert gas between the slag discharge port of theslagging combustion furnace and the surface of the slag cooling water.

As described above, the gas blowing means is provided to blow air orinert gas between the slag discharge port of the slagging combustionfurnace and the surface of the slag cooling water, thus preventinggas-liquid contact of exhaust gas and the slag cooling water. Therefore,the slag cooling water is prevented from being deteriorated in quality.

According to one aspect of the present invention, the system furthercomprises a gas mixture line for drawing a gas mixture of exhaust gasdischarged from the slag discharge port of the slagging combustionfurnace and the air or inert gas blown from the gas blowing means andsupplying the gas mixture into the slagging combustion furnace.

As mentioned above, the gas mixture line is provided to draw a gasmixture from the slag discharge port and to supply the gas mixture intothe slagging combustion furnace. The gas mixture line draws the air orinert gas blown between the slag discharge port and the surface of theslag cooling water and also steam evaporated from the slag coolingwater, thus preventing the slag discharge port and its vicinity frombeing cooled. The line also draws the exhaust gas having a hightemperature through the slag discharge port from the slagging combustionfurnace, thus keeping the slag discharge port and the portion around theslag discharge port at a high temperature. If the gas that has beenblown in is the air, because the air is supplied through the gas mixtureline into the slagging combustion furnace, the air can be utilized ascombustion air.

According to one aspect of the present invention, the system furthercomprises a flow control means provided in the gas mixture line forcontrolling the flow rate of the gas mixture drawn by the gas mixtureline.

As mentioned above, the flow control means can regulate the flow rate ofthe gas mixture drawn from the slag discharge portion.

According to one aspect of the present invention, the system furthercomprises a temperature sensor provided in the gas mixture line formeasuring the temperature of the gas mixture in the gas mixture line;wherein the flow control means is operated on a basis of an output ofthe temperature sensor to control the flow rate of the gas mixture drawnby the gas mixture line to equalize the temperature of the gas mixtureline with a set temperature.

The set temperature has a lower limit which is higher than the dew pointof hydrogen chloride contained in the exhaust gas for preventinglow-temperature corrosion. The set temperature has an upper limit whichis determined depending on the allowable temperatures of pipes and afan. Usually, the set temperature is set in a temperature range in whichinexpensive carbon steel can be used. Specifically, the gas mixture lineis preferably controlled in the range of 110 to 350° C.

As described above, the temperature sensor is provided to measure atemperature of the gas mixture, and the flow control means controls therate of the gas mixture drawn by the gas mixture line, thus keeping thetemperature of the gas mixture line at the set temperature on a basis ofthe output from the temperature sensor. If the set temperature is set toa value equal to or lower than the allowable temperature of the fanprovided in the gas mixture line, then the temperature of the gasmixture line can be kept equal to or lower than the allowabletemperature of the fan, and low-temperature corrosion of ducts of thegas mixture line and the fan is prevented.

According to an ash melting system of the present invention, slagdischarged from a slagging combustion furnace is supplied together withslag cooling water to a water tank having a settling and separatingfunction, the slag which has been settled and separated is removed froma bottom of the water tank and conveyed above the surface of the slagcooling water in the water tank, and then the slag is cleaned bycleaning water supplied from the cleaning water supply system.

With the above arrangement, harmful impurities such as heavy metalsattached to the surfaces of the water-quenched slag can be removed fromthe water-quenched slag, and hence the water-quenched slag of goodquality can be recovered.

Furthermore, even if the exhaust gas discharged together with the moltenslag from the slagging combustion furnace is not completely preventedfrom contacting the slag cooling water, the same cleaning effect can beobtained.

According to one aspect of the present invention, there is provided amethod of operating an ash melting system for melting ash into moltenslag and discharging the molten slag from a slag discharge port in aslagging combustion furnace, and producing water-quenched slag bybringing the molten slag into contact with slag cooling water, themethod comprising: blowing air or inert gas between the slag dischargeport of the slagging combustion furnace and the surface of the slagcooling water to prevent gas-liquid contact of exhaust gas dischargedfrom the slagging combustion furnace and the slag cooling water.

As described above, when the air or inert gas is blown between the slagdischarge port of the slagging combustion furnace and the surface of theslag cooling water, the exhaust gas is prevented from contacting theslag cooling water, and hence the slag cooling water is prevented frombeing lowered in quality. The water-quenched slag is thus prevented frombeing lowered in quality due to a deterioration in the quality of theslag cooling water.

According to another aspect of the present invention, there is provideda method of operating an ash melting system for melting ash, comprising:producing water-quenched slag from molten slag discharged from aslagging combustion furnace by bringing the molten slag into contactwith slag cooling water; supplying the water-quenched slag together withslag cooling water to a water tank having a settling and separatingfunction; removing the settled water-quenched slag from a bottom of thewater tank to separate the water-quenched slag from the slag coolingwater; and supplying cleaning water supplied from a cleaning watersupply system onto the water-quenched slag to clean the water-quenchedslag after the water-quenched slag is removed from the bottom of thewater tank and is conveyed above the surface of the slag cooling waterin the water tank.

As described above, after the water-quenched slag is removed from thebottom of the water tank, the water-quenched slag is cleaned by thecleaning water supplied from the cleaning water supply system.Consequently, harmful impurities such as heavy metals attached to thesurfaces of the water-quenched slag can be removed from thewater-quenched slag, and hence the water-quenched slag of good qualitycan be recovered.

According to one aspect of the present invention, there is provided agasification and slagging combustion system of wastes comprising: agasification furnace for gasifying wastes to generate gasificationproducts; a slagging combustion furnace for combusting the gasificationproducts to produce molten slag; a water-quenched slag producingmechanism for producing water-quenched slag by bringing slag dischargedfrom the slagging combustion furnace into contact with slag coolingwater; and a gas blowing means for blowing air or inert gas between aslag discharge port of the slagging combustion furnace and the surfaceof the slag cooling water.

As described above, the gas blowing means is provided to blow the air orinert gas between the slag discharge port of the slagging combustionfurnace and the surface of the slag cooling water, thus preventingexhaust gas discharged from the slagging combustion furnace through theslag discharge port from contacting the slag cooling water. Therefore,the gasification and slagging combustion system can be constructed suchthat the slag cooling water is prevented from being lowered in quality.

According to another aspect of the present invention, there is provideda gasification and slagging combustion system of wastes comprising: agasification furnace for gasifying wastes to generate gasificationproducts; and a slagging combustion furnace for combusting thegasification products to produce molten slag, wherein water-quenchedslag is produced by bringing the molten slag discharged from theslagging combustion furnace into contact with slag cooling water, thewater-quenched slag is supplied together with the slag cooling water toa water tank having a settling and separating function, and the settledwater-quenched slag is removed from a bottom of the water tank toseparate the water-quenched slag from the slag cooling water; whereincleaning water supplied from a cleaning water supply system is suppliedonto the slag to clean the slag after the slag is removed from thebottom of the water tank and is conveyed above the surface of the slagcooling water.

According to the gasification and slagging combustion system of wastes,the water-quenched slag is removed from the bottom of the water tank,and then the cleaning water supplied from the cleaning water supplysystem is supplied to the water-quenched slag to remove harmfulimpurities such as heavy metals attached to the surfaces of thewater-quenched slag, and hence the water-quenched slag of good qualitycan be recovered.

BRIEF DESCRIPTION OF DRAWINGS

FIG. 1 is a schematic view of a conventional melting furnace apparatushaving a swirling-type slagging combustion furnace (melting furnace), awater quenching trough, and a slag separating conveyor apparatus;

FIG. 2 is a schematic view of a melting system having a swirling-typeslagging combustion furnace, a water quenching trough, and a slagseparating conveyor apparatus according to the present invention;

FIG. 3 is a schematic view showing a slag discharge port and a portionaround the slag discharge port in a slagging combustion furnaceaccording to the present invention;

FIG. 4 is a schematic view of a melting system having a swirling-typeslagging combustion furnace, a water quenching trough, and a slagseparating conveyor apparatus according to the present invention;

FIG. 5 is a schematic view of a melting system having a swirling-typeslagging combustion furnace and a slag separating conveyor apparatusaccording to the present invention; and

FIG. 6 is a schematic view showing a slag discharge port and a portionaround the slag discharge port in a slagging combustion furnaceaccording to the present invention.

DETAILED DESCRIPTION OF THE INVENTION

Next, embodiments of the present invention will be described withreference to the drawings. FIG. 2 is a schematic view showing agasification and slagging combustion system having a swirling-typeslagging combustion furnace, a water quenching trough, and a slagseparating apparatus according to the present invention. Thegasification and slagging combustion system has a swirling-type slaggingcombustion furnace 10, a water quenching trough 30, and a slagseparating apparatus 50. The swirling-type slagging combustion furnace10 comprises a primary combustion chamber 11, a secondary combustionchamber 12, and a tertiary combustion chamber 13. A produced gas 111produced by pyrolysis of wastes and containing char and tar isintroduced into the upper part of the primary combustion chamber 11, ismixed with a gas 115 for combustion, and moves into the secondarycombustion chamber 12 while it is combusted. In the secondary combustionchamber 12, the gas is combusted at a high temperature of 1300 to 1450°C. Then, the gas passes through the tertiary combustion chamber 13 andbecomes exhaust gas 113, and the exhaust gas 113 is then discharged to awaste heat boiler (not shown).

The produced gas 111 (combustible gas containing unburned carbon andash) produced by pyrolysis of wastes and containing char and tar isintroduced into the upper part of the primary combustion chamber 11 in adirection tangential to an axis of the primary combustion chamber 11,thereby forming a swirling flow in the primary combustion chamber 11.The swirling flow causes the ash to be collected on the wall surface ofthe primary combustion chamber 11. The collected ash is melted at a hightemperature to form molten slag 121, and the molten slag 121 falls froma slag discharge port 14 through a slag discharge chute 21 into thewater quenching trough 30. The primary and secondary combustion chambers11 and 12 have blowing ports directed to introduce a gas for combustioninto the primary and secondary combustion chambers 11 and 12 in adirection tangential to axes of the primary and secondary combustionchambers 11 and 12. The molten slag 121 which has fallen into the waterquenching trough 30 is brought into contact with slag cooling water 152in the water quenching trough 30 to form water-quenched slag 122. Theformed water-quenched slag 122 is delivered into the slag separatingapparatus 50. In the slag separating apparatus 50, the water-quenchedslag 122 is scraped by scrapers 53 of a separating conveyor 52 and isremoved.

The gasification and slagging combustion system also has a gas blowingline 131 for blowing air (purge air) or inert gas (purge inert gas) at adischarge end of the water quenching trough 30. The gas blowing line 131blows the air or inert gas 132 to the lower end of the flow of the slagcooling water 152 (the lower end of the slag-granulating water surface).The introduced air or inert gas 132 flows along the slag-cooling watersurface into a region between the slag discharge port 14 of theswirling-type slagging combustion furnace 10 and the slag-cooling watersurface. The air or inert gas 132 thus introduced is effective toprevent the exhaust gas 112 flowing in through the slag discharge port14 from contacting the slag cooling water 152.

In this manner, by preventing gas-liquid contact of the slag coolingwater 152 and the exhaust gas 112, the slag cooling water 152 isprevented from being lowered in quality.

Because the slag cooling water 152 is prevented from being lowered inquality, the water-quenched slag 122 is also prevented from beinglowered in quality, i.e., from being lowered in quality by contaminantsof the contaminated slag cooling water which would otherwise be attachedto the surfaces of the water-quenched slag.

The air or inert gas 132 blown toward the lower end of theslag-granulating water surface of the water quenching trough 30 iseffective to purge the exhaust gas 112. A plurality of blowing ports maybe provided in the water quenching trough 30 for effectively purging theexhaust gas 112 or preventing the air or inert gas 132 from forminglocalized flows.

In the gasification and slagging combustion system, the water-quenchedslag 122 produced in the water quenching trough 30 is introduced into awater tank 51 of the slag separating apparatus 50. The water tank 51 hasa slag settling capability. The settled water-quenched slag is scrapedby the scrapers 53 and removed from the bottom of the water tank 51, andseparated from the slag cooling water. After the separatedwater-quenched slag is scraped and removed from the bottom of the watertank and conveyed above the water surface, the water-quenched slag iscleaned by cleaning water which is supplied from a cleaning water line161 and sprayed by a spraying nozzle 55. Thereafter, the water-quenchedslag 122 is conveyed by the separating conveyor 52, and discharged froma slag discharge opening 54.

In this manner, after the water-quenched slag is conveyed out of thebottom of the water tank 51, the water-quenched slag is cleaned by thesprayed cleaning water supplied from the cleaning water supply system.Consequently, harmful impurities such as heavy metals attached to thesurfaces of the water-quenched slag can be removed from thewater-quenched slag, and hence the water-quenched slag 122 of goodquality can be recovered.

By spraying the cleaning water from the cleaning water line 161, thecleaning water infiltrates frictional components (sliding components) ofthe slag separating apparatus 50 and serves as a lubricant for thosefrictional components of the slag separating apparatus 50. Therefore,the cleaning water is effective to reduce noise and wear of the slagseparating apparatus 50.

The method for cleaning water-quenched slag 122 in the slag separatingapparatus 50 is not limited to the method for supplying the cleaningwater from the spraying nozzle 55. Any method capable of cleaning thewater-quenched slag 122 which has been conveyed out of the slag coolingwater 152 in the water tank 51 may be used.

Even if a means for preventing the gas-liquid contact of the exhaust gas112 and the slag cooling water 152 by blowing air (purge air) or inertgas (purge inert gas) from the gas blowing line 131 to the discharge endof the water quenching trough 30 is provided, the slag cooling water 152is not fully effective to prevent the slag cooling water 152 from beingcontaminated on a long-term basis. However, as in the embodiment of FIG.2, using the spraying nozzle 55 together with the gas blowing line 131is effective to recover the water-quenched slag of good quality.

Further, as shown in FIG. 2, the slag discharge chute 21 has a suctionport 23 for drawing in a mixture of the air or inert gas 132 introducedinto the water quenching trough 30 and the exhaust gas 112. The suctionport 23 is connected to a gas mixture line 141 which has a damper 24 forcontrolling the flow rate of the gas mixture drawn from the suction port23 and a suction fan 22. The suction fan 22 has an outlet connected to agas mixture blowing line 142 for blowing the gas mixture into thetertiary combustion chamber 13 of the slagging combustion furnace 10.

Further, a temperature sensor 25 is provided in the gas mixture line141, and the output of the temperature sensor 25 is supplied to atemperature controller 26 which controls the opening of the damper 24and/or the rotational speed of a drive motor M of the suction fan 22 sothat a flow rate of the gas mixture is controlled to keep the gasmixture line 141 at a predetermined set temperature.

As described above, the temperature sensor 25 is provided in the gasmixture line 141 to control the circulating flow rate of the air orinert gas 132 and the exhaust gas 112 in order to keep the temperatureof the gas mixture line 141 at a set temperature. Thus, the temperatureof the gas mixture line 141 can be lowered to a allowable temperature ofthe suction fan 22. By keeping the gas mixture line 141 at a temperatureequal to or higher than the dew point of hydrogen chloride contained inthe exhaust gas, an occurrence of low-temperature corrosion of ductswhich define the gas mixture line 141 and the gas mixture blowing line142, and the suction fan 22 is prevented.

If a gas blown from the gas blowing line 131 is air, then the air issupplied as combustion air through the gas mixture blowing line 142 tothe tertiary combustion chamber 13 of the slagging combustion furnace10.

In the above embodiment, the temperature controller 26 controls theopening of the damper 24 and/or the rotational speed of the drive motorM for driving the section fan 22 to control the rate of the gas mixture.However, the temperature controller 26 may be used to control the rateof the air or inert gas 132 introduced from the gas blowing line 131 orcontrol the rate of the exhaust gas through the gas mixture line 141while keeping the rate of the air or inert gas 132 constant. That is,either the rate of the air or inert gas 132 introduced from the gasblowing line 131 or the rate of the exhaust gas 112 through the gasmixture line 141 may be controlled.

Further, in the slagging combustion furnace 10 shown in FIG. 2, atemperature sensor may be installed near the slag discharge port 14 ofthe slagging combustion furnace 10, and based on an output signal of thetemperature sensor, the temperature controller 26 may control theopening of the damper 24 and/or the rotational speed of the drive motorM for driving the suction fan 22 to control the rate of the gas mixtureof the air or inert gas 132 and the exhaust gas 112, thereby keeping thetemperature of the slag discharge port 14 at a set temperature.

In this manner, by providing the temperature sensor near the slagdischarge port 14 and controlling the flow rate of the gas mixture inorder to keep the temperature of the slag discharge port 14 and theportion around the slag discharge port 14 at a set temperature or tokeep the amount of slag attached to the slag discharge port 14 at apredetermined amount or less, based on an output signal from thetemperature sensor serving as a flow control means, the slag dischargeport 14 can have a desired level of dischargeability of molten slag. Forexample, by varying the rate of the gas mixture while keeping thetemperature of the mixture of the exhaust gas and the air or inert gasconstant, while heat resistance of the suction fan is ensured andlow-temperature corrosion of the suction fan is prevented fromoccurring, a desired level of dischargeability of molten slag can bemaintained.

When the slag discharge port is clogged for some reason, a burner 170 isoperated to produce flames 171 to melt away the slag attached to theslag discharge port 14 and the portion around the slag discharge port14, as shown in FIG. 3. Because the amount of a high-temperature gasproduced is greater at this time than at a normal operation of theswirling-type slagging combustion furnace, only the air or inert gas 132that is introduced is not sufficient enough to keep the gas mixture at adesired temperature, and the gas mixture tends to increase itstemperature unduly. In order to solve this problem, there is provided acooling water injecting mechanism having cooling water nozzles 173 forinjecting cooling water 172 into the slag discharge chute 21. When themixture gas suffers an undue temperature increase, cooling water isinjected into the slag discharge chute 21 to lower the temperature ofthe gas mixture. In the case where the amount of a high-temperature gasproduced is greater at this time than at a normal operation, the air orinert gas 132 may be introduced in an increased amount to cool thehigh-temperature gas. However, the air or inert gas 132 introduced in anincreased amount would bring about an increase in the amount of the gasmixture, resulting in an uneconomical gas circulation system design.Furthermore, the air or inert gas 132 may be reduced in an amountdepending on the scale of the furnace. The cooling water injectingmechanism which is used at all times in combination with theswirling-type slagging combustion furnace 10 is effective to reduce thetemperature of the exhaust gas 112 and allows the gasification andslagging combustion system to have a wider range of applications.

The slag discharge port 14 may be cooled by water cooling tubes (watercooling structure) for increasing the durability of refractory materialfor defining the slag discharge port 14. The slag discharge port 14 thuscooled may be prevented from suffering an undue temperature rise. Inview of the possibility of an undue temperature reduction of moltenslag, the swirling-type slagging combustion furnace 10 should preferablybe combined with an in-furnace ITV (Industrial Television) system, i.e.,a remote monitoring system for monitoring the state of molten slag. Thein-furnace ITV system has an ITV which may be located at a position formonitoring the slag discharge port.

FIG. 4 is a view showing a melting system according to anotherembodiment of the present invention.

The melting system shown in FIG. 4 differs from the melting system shownin FIG. 2 in that a heat exchanger 42 is provided in a slag coolingwater circulation line 151, the slag cooling water 152 in the water tank51 is delivered to the heat exchanger 42 by a pump 41. By introducingcooling water 153 from the outside, heat exchange between the coolingwater 153 and the slag cooling water 152 is performed to cool the slagcooling water 152.

The cooling water 153 is introduced through a conduit having a controlvalve 43 which is controlled by a controller 45 that monitors thetemperature of the slag cooling water 152 based on an output signal froma temperature sensor 44. The controller 45 controls the opening of thecontrol valve 43 to control the rate of the cooling water 153 to keepthe slag cooling water 152 at a set temperature.

The temperature of the slag cooling water 152 is increased when the slagcooling water 152 is brought into contact with the high-temperaturemolten slag 121. As the temperature of the slag cooling water 152 isincreased, the amount of the slag cooling water 152 which is evaporatedis also increased, and hence a large amount of replenishing water isrequired.

The increase of the amount of the evaporated slag cooling water 152causes the temperature of the gas mixture in the slag discharge chute 21to be lowered. In order to keep the gas mixture in the gas mixture line141 constant, it is necessary to draw in a large amount of exhaust gas112. Consequently, the gas mixture line 141, the gas mixture blowingline 142, and the suction fan 22 become large in size, resulting in anincrease in the construction cost.

Further, the slag separating apparatus 50 also suffers a temperatureincrease, and this temperature increase is not desirable from thestandpoint of safety and working environments.

According to the present invention, the heat exchanger 42 is provided inthe slag cooling water circulation line 151, and heat exchange betweenthe slag cooling water 152 in the water tank 51 of the slag separatingapparatus 50 and the cooling water 153 supplied from the outside isperformed to keep the slag cooling water 152 in the water tank 51 of theslag separating apparatus 50 in a set (or preset) temperature range forthereby suppressing evaporation of the slag cooling water 152.

FIG. 5 schematically shows a melting system according to anotherembodiment of the present invention.

In the embodiment shown in FIGS. 2 and 4, the molten slag 121 dischargedfrom the slag discharge port 14 is discharged through the waterquenching trough 30 into the slag separating apparatus 50. However, thewater quenching trough 30 may not necessarily be required. For example,as shown in FIGS. 5 and 6, molten slag 121 discharged from the slagdischarge port 14 is directly discharged into the slag cooling water 152in the slag separating apparatus 50. The air or inert gas 132 blown fromthe gas blowing line 131 is introduced between the slag discharge port14 and the water surface of the slag cooling water 152.

In the above embodiments, the slagging combustion furnace comprises aswirling-type slagging combustion furnace. However, the presentinvention is not limited to a swirling-type slagging combustion furnace,but is applicable to a melting furnace apparatus having a meltingfurnace for melting ash into molten slag, such as a plasma meltingfurnace, a surface melting furnace, or the like.

A gasifying apparatus in the gasification and slagging combustion systemaccording to the present invention has a gasification furnace forgasifying combustibles such as wastes, although such gasificationfurnace is not shown. The gasification furnace may comprise any desiredgasification furnace such as an internal circulating fluidized-bedgasification furnace, an external circulating fluidized-bed gasificationfurnace, or a kiln furnace. In the fluidized-bed gasification furnace, afluidized medium such as sand, Olivin sand, or alumina is used, and afluidizing gas such as preheated air, air, oxygen-enriched air, or steamis introduced from an air diffuser plate or air diffuser pipes to form acirculating flow of the fluidized medium in a fluidized bed. Thecirculating flow of the fluidized medium may be oriented in anydirection and is expected to provide an effect to transfer heat in thefluidized bed and an effect to crush materials such as wastes to betreated. The direction of the circulating flow of the fluidized mediummay be designed depending on the position where incombustibles arewithdrawn from the furnace. Various materials including wastes aresupplied to the fluidized bed from the location above the fluidized bedin which the circulating flow of the fluidized medium is formed, andpyrolyzed and gasified in the fluidized bed. The gas, which accompaniesash and pulverized carbon, produced in the fluidized-bed gasificationfurnace is then introduced into the subsequent slagging combustionfurnace (melting furnace) of the gasification and slagging combustionsystem according to the present invention.

As described above, according to the present invention, the followingexcellent effects can be obtained.

(1) The gas blowing means is provided to blow air or inert gas betweenthe slag discharge port of the slagging combustion furnace and thesurface of the slag cooling water, thus preventing exhaust gas fromcontacting the slag cooling water. Therefore, the slag cooling water isprevented from being lowered in quality. The water-quenched slag isprevented from being lowered in quality due to a reduced quality of theslag cooling water, i.e., the water-quenched slag is prevented frombeing lowered in quality due to contamination of the slag cooling water.Further, the slag discharge port and the portion around the slagdischarge port is prevented from being cooled due to steam generated byevaporation of the slag cooling water.

(2) The gas mixture line (the gas mixture drawing/blowing line) isprovided to draw a mixed gas from the slag discharge portion of theslagging combustion furnace and to blow the mixed gas into the slaggingcombustion furnace. The gas mixture line draws the air or inert gasblown to the slag discharge portion and also steam produced byevaporation of the slag cooling water, thus preventing the slagdischarge port and the portion around the slag discharge port from beingcooled. The gas mixture line also draws the exhaust gas having a hightemperature through the slag discharge port, thus keeping the slagdischarge port and the portion around the slag discharge port at a hightemperature with the high-temperature exhaust gas and maintainingdischargeability of the slag. The air that has been blown in is suppliedthrough the gas mixture line into the slagging combustion furnace,particularly a tertiary combustion chamber of the slagging combustionfurnace, and can be utilized as combustion air.

(3) By providing the flow control means, the flow rate of the gasmixture drawn from the slag discharge portion can be controlled.

(4) By providing the temperature sensor in the gas mixture line, theflow control means controls the flow rate of the gas mixture so as tokeep the temperature of the gas mixture line at the set temperaturebased on the output from the temperature sensor. If the set temperatureis set to a value equal to or lower than the allowable temperature ofthe fan provided in the gas mixture line, then the temperature of thegas mixture line can be kept to be equal to or lower than the allowabletemperature of the fan. If the gas mixture line is operated at atemperature of the dew point of hydrogen chloride contained in theexhaust gas or higher, low-temperature corrosion of ducts which definethe gas mixture line and the suction fan connected thereto is prevented.

(5) Harmful impurities such as heavy metals attached to the surfaces ofthe water-quenched slag can be removed from the water-quenched slag bythe cleaning water supplied from the cleaning water supply system, andhence the water-quenched slag of good quality can be recovered.

Furthermore, even if the exhaust gas discharged together with the moltenslag from the slagging combustion furnace is not completely preventedfrom contacting the slag cooling water, the same cleaning effect can beobtained.

(6) When the air or inert gas is blown between the slag discharge portof the slagging combustion furnace and the surface of the slag coolingwater, the exhaust gas is prevented from contacting the slag coolingwater, and hence the slag cooling water is prevented from being loweredin quality. The water-quenched slag is thus prevented from being loweredin quality due to a reduced quality of the slag cooling water.

(7) After the water-quenched slag is scraped and removed from the bottomof the water tank and is conveyed above the surface of the slag coolingwater in the water tank, the water-quenched slag is cleaned by thecleaning water sprayed from the cleaning water supply system.Consequently, harmful impurities such as heavy metals attached to thesurfaces of the water-quenched slag can be removed from thewater-quenched slag, and hence the water-quenched slag of good qualitycan be recovered.

(8) The gas blowing means is provided to blow the air or inert gasbetween the slag discharge port of the slagging combustion furnace andthe surface of the slag cooling water, thus preventing exhaust gasdischarged from the slagging combustion furnace through the slagdischarge port from contacting the slag cooling water. Therefore, thegasification and slagging combustion system can be constructed such thatthe slag cooling water is prevented from being lowered in quality. Thewater-quenched slag is also prevented from being lowered in quality dueto a reduced quality of the slag cooling water.

(9) After the water-quenched slag is scraped and removed from the bottomof the water tank and is conveyed above the surface of the slag coolingwater, the cleaning water supplied from the cleaning water supply systemis sprayed over the water-quenched slag to remove harmful impuritiessuch as heavy metals attached to the surfaces of the water-quenchedslag. Therefore, the gasification and slagging combustion system whichcan recover the water-quenched slag of good quality can be constructed.

INDUSTRIAL APPLICABILITY

The present invention is applicable to a melting system for bringingmolten slag discharged from an ash melting furnace into contact withwater to produce water-quenched slag and a method of operating suchmelting system, and a melting system attached to a gasification andslagging combustion system for combusting and treating various wastesincluding municipal wastes, refuse-derived fuel (RDF), plastic wastes,waste FRP, biomass wastes, automobile wastes, waste oil, and the like.

1. An ash melting system comprising: a slagging combustion furnace formelting ash into molten slag and discharging the molten slag from a slagdischarge port; a slag separating apparatus for bringing the molten slaginto contact with slag cooling water to produce water-quenched slag, andfor separating the water-quenched slag from the slag cooling water; anda gas blowing member for blowing air or inert gas between said slagdischarge port of said slagging combustion furnace and the surface ofthe slag cooling water.
 2. A system according to claim 1, furthercomprising: a gas mixture line for drawing a gas mixture of exhaust gasdischarged from said slag discharge port of said slagging combustionfurnace and the air or inert gas blown from said gas blowing member, andfor supplying said gas mixture into said slagging combustion furnace. 3.A system according to claim 2, further comprising: a flow control memberprovided in said gas mixture line for controlling the flow rate of saidgas mixture drawn by said gas mixture line.
 4. A system according toclaim 3, further comprising: a temperature sensor provided in said gasmixture line for measuring the temperature of said gas mixture in saidgas mixture line; wherein said flow control member is operated based onan output of said temperature sensor to control the flow rate of saidgas mixture drawn by said gas mixture line to equalize the temperatureof said gas mixture line with a set temperature.
 5. The ash meltingsystem of claim 1, wherein said gas blowing member includes a gas inletport located below said slag discharge port and above the surface of theslag cooling water.
 6. The ash melting system of claim 1, wherein saidgas blowing member is arranged so as to introduce the air or inert gasto create a gas barrier between exhaust gas in said slagging combustionfurnace and the surface of the slag cooling water.
 7. The ash meltingsystem of claim 1, wherein said gas blowing member is arranged to blowthe air or inert gas in a direction from the surface of the slag coolingwater toward said slag discharge port.
 8. A method of operating an ashmelting system for producing water-quenched slag from molten slagdischarged from a slagging combustion furnace, and for then separatingthe water-quenched slag from slag cooling water, the method comprising:blowing air or inert gas between a slag discharge port of the slaggingcombustion furnace and the surface of the slag cooling water.
 9. Themethod of operating an ash melting system of claim 8, wherein saidblowing comprises blowing the air or inert gas in a direction from thesurface of the slag cooling water toward the slag discharge port. 10.The method of operating an ash melting system of claim 8, wherein saidblowing the air or inert gas comprises introducing the air or inert gasto create a gas barrier between exhaust gas in the slagging combustionfurnace and the surface of the slag cooling water.
 11. A gasificationand slagging combustion system comprising: a gasification furnace forgasifying wastes to generate gasification products; a slaggingcombustion furnace for combusting said gasification products to producemolten slag; and a gas blowing member for blowing air or inert gasbetween a slag discharge port of said slagging combustion furnace andthe surface of slag cooling water.
 12. The gasification and slaggingcombustion system of claim 11, wherein said gas blowing member includesa gas inlet port located below said slag discharge port and above thesurface of the slag cooling water.
 13. The gasification and slaggingcombustion system of claim 11, wherein said gas blowing member isarranged so as to introduce the air or inert gas to create a gas barrierbetween exhaust gas in said slagging combustion furnace and the surfaceof the slag cooling water.
 14. The gasification and slagging combustionsystem of claim 11, wherein said gas blowing member is arranged to blowthe air or inert gas in a direction from the surface of the slag coolingwater toward said slag discharge port.